Sorry, should have pointed that out. No, I don't see a log file.
There are no output files of any sort when scribble is done. I would
have anyway thought scribble was doing all this in some tmp directory
somewhere else.
Aha, I just found out that there's a scribble --latex option. I ran
that and it produced a .tex file, which went through pdflatex without
a problem (yes, I used the explicit path to pdflatex printed by
DrRacket), and the resulting PDF looks good. So the problem is
presumably in the interaction between scribble and pdflatex.
Running scribble --pdf in that same directory, however, still produces
the same error, reinforcing my belief that scribble is running
pdflatex in some temp directory where it's still looking for a
non-existent .log.
[Incidentally, I found out about --latex from running scribble --help.
This claims that the default is --text. I believe this is wrong: the
default appears to actually be --html.]
Shriram